Injection apparatus

ABSTRACT

An injection apparatus of a plunger type for injecting reinforced materials such as BMC is of a single barrel type or a double barrel type comprising a rotatable plunger disposed in the barrel. A check valve means for preventing a back flow of the materials in a metering process is provided such that it is closed when the plunger is actuated to move axially for injection.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an injection apparatus, particularly aninjection apparatus preferably used for injecting reinforced plastics orbulk molding compounds (BMC) such as thermosetting resins includingglass fibers.

2. Description of the Related Art

BMC, such as unsaturated polyester resin containing glass fibers, havebeen provided having various compositions and properties as needed forspecific usages and molding processes. In molded products of BMC, themechanical properties have a correlationship with the states of thefibers in the products, and the mechanical strength of the products isenhanced as the fibers are longer and are not bent. The fiber length inthe product is related to not only the starting glass fibers but also toa molding process per se. In this regard, it is desired to adopt amolding process which causes the least possible damage to the glassfibers therein, in order to improve the mechanical properties of theproduct.

A plunger type molding apparatus does less damage to the glass fibers,and less bending of the fibers occurs, compared with a screw typemolding apparatus. However, the use of such plunger type moldingapparatuses has decreased, in spite of the above advantages. This isbecause the construction of the plunger type molding apparatus isdisadvantageous, as explained hereinbelow with reference to FIG. 2 andFIG. 3 attached hereto.

Referring to FIG. 2 showing a conventional plunger type injectionapparatus, the apparatus 1 comprises a stuffer or feeder 3 and a barrel4 connected thereto by an elbow conduit 2. The stuffer 3 is providedwith a feed cylinder 5 having a piston which forms a plunger 6 disposedin the stuffer 3 for reciprocating movement. An injection cylinder 7 isprovided with a piston forming an injection plunger 8 slidably disposedin the barrel 4. The barrel 4 has an injection nozzle or orifice 10formed at the free end thereof and a feed inlet 9 for admitting materialfrom the stuffer 3 opening at an intermediate portion thereof in aposition relatively close to the nozzle 10. A ball 11 is provided toform, in combination with the feed inlet 9, a check valve for preventinga back flow of the material. With the above arrangement, materials 12are charged from the stuffer 3, and the plunger 6 is forced to moveforward by the feed cylinder 5. The materials 12 are forced to passthrough the elbow 2 and enter the barrel 4 through the feed inlet 9.While the supplied materials in the barrel are prevented from flowingback to the stuffer 3 by the check valve having the ball 11, theinjection cylinder 7 is actuated to force the injection plunger 8 tomove forward, to thereby inject the materials into a mold (not shown).

FIG. 3 shows another conventional plunger type apparatus in which thesame numerals denote the same members or elements as those of theapparatus in FIG. 2. The apparatus shown in FIG. 3 has some differencesfrom the first apparatus as shown in FIG. 2, in that the correspondingfeed inlet 9A opens to the barrel 4A at the other end thereof far fromthe nozzle 10, and a check valve is not provided.

According to the apparatus shown in FIG. 2, it is noted that the feedinlet 9 is located close to the nozzle 10, with the result that stablemetering of the materials 12 is easily effected since the materials canbe supplied into the barrel 4 in a metering process, while beingsubjected to a back pressure exerted by the injection cylinder 7. Inturn there is a disadvantage in that the materials 12 are likely toremain or stay in the barrel 4, since a leading part of the materials islikely to advance toward the injection plunger 8 and a following part ofthe materials is forced to move toward the nozzle 10, with the resultthat the subsequent materials are injected before all of the precedingmaterials are injected. Further, a sealing of the plunger 8 is likely tobe damaged since the sealing must pass over the feed inlet in theinjection process.

The apparatus as shown in FIG. 3 has certain disadvantages in thatmetering of the materials 12 is unstable, and the involvement orentrainment of air in the materials is likely to occur. This is because,with the feed inlet 9A provided at the side of the injection plunger 8,each shot is carried out at each retirement of the injection plunger 8,with the result that a leading part of the materials entered in advancemust be ejected from the nozzle 10 before the following part of thematerials, but the injection cylinder is not allowed to exert a backpressure against the materials in the barrel.

SUMMARY OF THE INVENTION

An object of the present invention is to overcome the above mentioneddisadvantages of conventional plunger type injection apparatuses for usein producing molded products of reinforced materials such as BMC.

According to the present invention, there is provided a first kind of aninjection apparatus of a plunger type for injecting reinforced materialssuch as BMC. The first apparatus comprises: a single cylindrical barrelhaving an injection nozzle at a free front end thereof; a plungerdisposed in the barrel for axial reciprocating movement and rotation; astuffer of a jack for feeding the materials, the stuffer communicatingwith the barrel through a feed outlet thereof; check valve means forpreventing a back flow of the materials; a piston-cylinder arrangementfor axially actuating the plunger; and a motor means for rotating saidplunger, a metering or volume chamber having variable volume for thematerials being defined by the inner surface of the barrel, the freefront end thereof, the check valve means and the plunger. The materialsare forced to enter from the jack stuffer into the barrel, and theplunger is forced to rotate with the entered materials having freedom toaxially move rearward against a back pressure applied. The enteredmaterials pass through the check valve means and enlarge the meteringchamber. While the check valve means is forced to close to prevent aback flow of the metered materials from the metering chamber, theplunger is forced to axially move forward to thereby inject the meteredmaterial out of the nozzle.

In the above apparatus, preferably the plunger may have a constrictedlocal part at a front portion thereof and the check valve means maycomprise the constricted plunger part forming a valve chamber and a ringforming a movable valve member slidably and rotatably fitting the innersurface of said barrel and encircling the constricted plunger part witha space gap. The check valve means is forced to close when the plungeris forced to axially move forward for the injection.

Alternatively, a rear end portion of the plunger may be enlarged so asto slidably and rotatably fit the inner surface of the barrel, and avalve chamber receiving a ball forming a movable valve member therein ismounted between the barrel and the stuffer to communicate therebetween.The valve chamber has axial openings for the communication at its barrelside and stuffer side walls and grooves formed at its barrel side innerwall and communicating with the barrel side opening. The check valvemeans is closed when the ball covers the stuffer side opening, but iskept open when the ball covers the barrel side opening. The ball valvemember is forced to move toward the stuffer side opening when themetered materials are injected, to thereby close the check valve means.

Further, the jack stuffer may have an axially cylindrical portioncommunicating with the feed outlet. The barrel is an axial extensionrotatably and slidably disposed in the cylindrical stuffer portion witha sealing provided between the barrel and the stuffer. A second motormeans is provided for rotating the barrel. The check valve meanscomprises the cylindrical stuffer portion forming a valve chamber and alocal portion of the barrel having a feed inlet opening and covered bythe cylindrical stuffer portion. The local barrel portion forms amovable valve member. The second motor means is activated to rotate thebarrel over a certain angle to thereby close the check valve means.

With the above alternative apparatus, the plunger may have an enlargedrear portion slidably and rotatably fitting the inner surface of thebarrel and a local portion adjacent the enlarged end portion, and thelocal plunger portion has a helically encircling projection.

According to the present invention, there is provided a second kind ofan injection apparatus of a plunger type for injecting reinforcedmaterials such as BMC. The second apparatus comprises: a double barrelarrangement comprising an outer cylindrical barrel having an injectionnozzle at a free front end thereof and an inner cylindrical barrelslidably disposed in and fitting the inner surface of the outer barrel;a stuffer of a jack for feeding the materials, the inner barrelcommunicating with the interior of the outer barrel at the free frontend thereof and with a feed outlet of the jack stuffer at the other rearend portion thereof; a plunger disposed in the double barrel arrangementfor axial reciprocating movement and rotation; check valve means forpreventing a back flow of the materials; a piston-cylinder arrangementfor actuating the movable inner barrel relative to the outer barrel; ajack for activating the plunger relative to the inner barrel; a motormeans for rotating the plunger. The plunger and the inner barrel incombination are activated by cooperation of the piston-cylinderarrangement and the jack to axially move forward. A metering or volumechamber having a variable volume for the materials is defined by theinner surface of the outer barrel, the free front end thereof, the checkvalve means and the inner barrel. The materials are forced to enter fromthe jack stuffer into the inner barrel, and the plunger is forced torotate with the entered materials having freedom to axially moverearward against a back pressure applied together with the inner barrel.The entered materials pass through the check valve means and enlarge themetering chamber. While the check valve means is forced to close toprevent a back flow of the metered material from the metering chamber,the plunger and the inner barrel in combination are forced to axiallymove forward to thereby inject the metered materials out of the nozzle.

With above second apparatus, preferably the plunger may have an enlargedhead portion extending out of the free front end of the inner barrel.The check valve means comprises the front inner barrel end forming avalve seat and the enlarged plunger head forming a movable valve memberfor seating at the valve seat. The jack for the plunger activates thevalve member to close the check valve means.

Alternatively, the inner barrel may have a constricted hollow head. Theplunger has a tapered head located in the interior of the inner barrel.The check valve means comprises the constricted inner barrel headforming a valve seat and the tapered plunger head forming a movablevalve member for seating at the valve seat. The jack for the plungeractivates the valve member to close the check valve means.

Further, the inner barrel may have a hollow head portion forming a valvechamber therein, where a ball forming a movable valve member isreceived. The valve chamber has axial openings at its front and rearwalls and grooves formed at its front inner wall and grooves formed atthe front inner wall and communicating with the front opening. The checkvalve means is closed when the ball covers the rear opening but keptopen when the ball covers the front opening. The ball valve member isforced to move rearward relative to said inner barrel when the meteredmaterials are injected, thereby closing the check valve means.

Still further, the inner barrel may have a hollow head portion forming avalve chamber therein and a valve member pivotable about an axisperpendicular to that of the inner barrel. In this case, driving meansis provided to actuate the pivotable valve member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic axially sectional view of a plunger type injectionapparatus according to the present invention, the apparatus being asingle barrel type;

FIG. 2 is a schematic axially sectional view of a prior art plunger typeinjection apparatus for reinforced materials;

FIG. 3 is a similar view of another, similar-type prior art apparatus;

FIG. 4, FIG. 5, and FIG. 6 are schematic axially sectional views of amodified apparatus of FIG. 1 partially showing the modificationsthereof, respectively;

FIG. 7 is a view corresponding to FIG. 1, showing another injectionapparatus of plunger type according to the present invention, theapparatus being a double barrel type;

FIG. 8, FIG. 9, and FIG. 10 are views corresponding to FIGS. 4 to 6,showing modifications of the double barrel type apparatus of FIG. 7,respectively;

FIG. 11 and FIG. 12 are views corresponding to FIG. 1 showing othermodified single barrel type apparatuses of according to the presentinvention, respectively; and,

FIG. 13 and FIG. 14 are cross-sectional views of the apparatus shown inFIG. 12 taken along the line XIII--XIII thereof, showing axialoperations of a check valve provided in the apparatus, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 showing a first embodiment of the present invention,a plunger type injection apparatus comprises a single barrel 22 having acylindrical extension. The barrel 22 has a circumferential heater (notshown) imparting a relatively low heat to the barrel 22 and a nozzle 21at a free front end of the barrel, mounted for a mold (not shown). Aplunger 24 is mounted in the barrel 22 with a space gap for axialreciprocation and for rotation. The plunger 24 is provided with a checkring 23 slidably and rotatably fitted in the inner surface of the barrel22 and encircling a constricted part of the plunger 24 formed at a freefront end portion thereof. A head of the plunger 24 adjacent to theconstricted part has grooves 24a at its circumferential surface, whichallow the feed materials to pass over the plunger head, even if the ring23 is in contact with the plunger head. The plunger 24 and the ring 23,in combination, form a check valve which prevents a back flow ofreinforced materials to be injected through the barrel 22 and nozzle 21into the mold. The plunger 24 is further provided with a conventionalpiston-cylinder device (not shown) and a hydrodynamic motor (not shown)for axial and rotational movement thereof.

The plunger 24 has an enlarged part 25 at an intermediate portionthereof, slidably and rotationally fitted in the inner surface of thebarrel 22. A space gap between the plunger 24 and the barrel 22 allowsthe materials to move axially along the plunger 24 toward the nozzle 21.A single pitch screw thread 26 is formed to project from the surface ofthe plunger 24 in the vicinity of the enlarged part 25 at a front sidethereof. The screw thread 26 is designed so that it forces the materialswhich were fed from the stuffer described below, to move forward uponnormal rotation of the plunger 24. Accordingly, the reinforced materialsare prevented from staying in the same place within the plunger 24 andby-passing along the barrel 22, whereby a unification or homogenity ofthe reinforced materials including glass fibers is attained. In thisregard, the screw 26 is designed to be located at a feed outlet of thestuffer.

Another screw thread 29 is formed at the rear of the plunger enlargedpart 25 in order to smoothly discharge out of the barrel a part of thematerials, which materials may have leaked through the space gap at thefront of the enlarged part 25 into the rear of the enlarged part 25through a clearance between the enlarged part 25 and the barrel 22. Inthis regard, the rear screw 29 is designed to have an angle which is thereverse of that of the front screw thread 26.

Numeral 27 denotes the above mentioned stuffer, which comprises a jackhaving a vertical axis perpendicular to that of the barrel 22. Thestuffer jack 27 is mounted on th barrel 24 and comprises a piston orplunger 30 and a cylinder 31 having feed outlet 28 at a lower end andthereof communicating with the barrel 22 at a feed inlet thereof.

With the apparatus as shown in FIG. 1, the plunger 24 is firstpositioned at a forward limit of movement and is rotated at 25 to 150r.p.m. Reinforced materials such as BMC are charged in the stuffer 27,and extruded downward by the stuffer plunger 30. BMC is fed into thebarrel 22 and is forced to move forward in the space gap between thebarrel 22 and the plunger 24. The fed materials are forced to passthrough the check valve involving the ring 23, and are stored in ametering or volume chamber formed in the barrel 22 between the nozzle 21and the head of the plunger 24. In this feeding or metering process, theplunger is free to move rearwardly under a back pressure applied, and asthe metering chamber is increasingly filled with BMC, the plunger iscorrespondingly moved rearwardly by the back pressure generated thereby.When BMC are used as the materials, the temperature of the materials maybe set to 40° to 60° C., and the temperature of the mold may be set to160° C. The extruding pressure applied to the materials in the stuffer27 may be in an order of 1 kg/cm² to 140 kg/cm³. The back pressure maybe exerted by controlling the hydraulic pressure of oil in a rearchamber of the piston-cylinder device. Alternatively, such a backpressure may be exerted due to friction occurring between the enlargedpart 25 and the barrel 22.

In the above arrangement, rotation of the plunger 24 causes thematerials to be uniformalized or homogenized and prevents the materialsfrom taking a by-pass flowpath. The rotating screw thread 26 and theextruding stuffer plunger 30 cooperate to cause the materials to betransferred smoothly in the barrel 22 without remaining in localizedspots. When the volume chamber is increasingly filled with apredetermined amount of the materials, the rotation of the plunger 24 isstopped, and the piston-cylinder device is then activated to cause theplunger 24 to move forward and thereby inject the metered materials intothe mold through the nozzle 21. The check valve is opened during thefeeding and metering process, and is closed during the injectionprocess.

Modifications of the apparatus shown in FIG. 1 are indicated in FIGS. 4to 6. Referring to FIG. 4, the modification resides in that an enlargedpart 25 corresponds to that of FIG. 1, but extends right to the rear endof the plunger 24 so that it forms a rear portion per se of the plunger24. As a result, a second screw such as the screw 29 of FIG. 1 isomitted, and accordingly, the construction of the plunger become simplerthan that of FIG. 1.

Referring to FIG. 5, a modification is made to the apparatus of FIG. 4,and resides in that a helical projection 32 is formed in place of thescrew thread 26 at the surface of the plunger 24. The screw thread 26 ofFIG. 4 has relatively keen edges and thus these edges are likely todamage reinforced materials in comparison, if the materials containglass fibers. Conversely, the helical projection 32 has no edge, butinstead, has a relatively round profile. Such a profile will not damagethe glass fibers. Preferably, a ratio of a height h of the projection tothe space gap H between the front portion of the plunger 24 and thebarrel 22 is not more than 0.95 (h/H). A pluratity of such helicalprojections may be formed on the plunger 24.

Referring to FIG. 6, the modification made is different to those of FIG.4 and FIG. 5 in that both any of the screw thread 26 and the projection32 are omitted and, instead, an axial channel 33 is formed in theplunger 24 for cooling the materials around the plunger with watersupplied therein. This cooling means may prevent super-heating of localparts of the materials and also allow friction, occurring between thematerials and the barrel and between the materials and the plunger, tobe controlled, to thereby improve performance of the material feed. Anadmixing effect due to the plunger as shown in FIG. 6 for the materialsin the barrel 24 is reduced in comparison with those of the plungers 24as shown in FIGS. 4 and 5. However, the admixing effect is obtained tosome extent due to cooperation of the rotation of the plunger 24 and theextruding pressure exerted by the stuffer plunger 30. The modificationas shown in FIG. 6 is also advantageous in that omission of the screwthread 26 or the projection 32 simplifies working of the surface of theplunger 24.

Referring to FIG. 7, showing a second embodiment of the presentinvention, a plunger type injection apparatus is a double barrel typehaving an outer stationary barrel 22A and an inner movable barrel 22Bslidably disposed in and fitting the outer barrel 22A. The stationaryouter barrel 22A has a nozzle 21 at the free front end and is fixed to astationary support 34A, which is integral with a base 34 of theapparatus. The apparatus base is movable relative to the mold so thatthe nozzle 21 can be placed in contact with the mold as needed. Aplunger 24 is mounted in the double type barrel for axial reciprocationand rotation with a space gap between the plunger 24 and the innerbarrel 22B. A hydrodynamic motor 35 for rotating the plunger 24 is fixedat the rear end thereof to a movable support 36, which is designed so asto be slidable along and on the apparatus base 34. The movable support36 is provided with a jack 37 having a piston rod 37A, which isconnected to a movable base 38 of the inner barrel 22B. The movable base38 is slidable along the apparatus base 34. The jack 37 is actuated tomove the plunger 24 forward or rearward relative to the inner barrel22B. The same stuffer 27 as that of FIG. 1 is provided and communicateswith the inner barrel 22B.

The inner barrel 22B has a conical opening 39 at the free front endthereof, forming a valve seat, and the plunger 24 has an enlarged head40, forming a movable valve member to be engaged at a tapered rear part41 thereof with a valve seat. The plunger head 40 and the conical barrelopening 39 form a check valve. A rearward movement of the plunger 24relative to the inner barrel 22B upon actuation of the jack 37 causesthe valve to be closed, to thereby prevent a back flow of the materials.When the plunger 24 moves relative to the inner barrel 22B, the checkvalve is opened. The slidable base 38 forms a piston-cylinder device 42having a piston rod 43 connected to the stationary base 34. The device42 is actuated so that the inner barrel 22B moves axially forward orrearward relative to the outer barrel 22A. While the valve is opened asshown in FIG. 7, the stuffer jack 27 is actuated to make a plunger 30extrude the materials from the stuffer into the inner barrel 22B andconcurrently the motor is actuated to rotate the plunger 24. This is afeeding and metering operation of the apparatus, in which the fedmaterials pass through the opened valve and are stored in a meteringchamber formed between the nozzle 21 and the plunger head 40 in theouter barrel 22A. As the volume of the metering chamber increases, theplunger and the inner barrel 22B, combined by means of the jack 37, moverearward relative to the outer barrel 22A against a back pressureapplied thereto. When a predetermined amount of the materials ismetered, the operation of the stuffer 27 is stopped and the jack 37 isactuated to make the plunger 24 move rearward relative to the innerbarrel 22B so that the valve is closed. While the valve is closed, onlythe piston-cylinder device 42 is actuated, to make the inner barrel 22B,in combination with the plunger 24, move forward and thereby inject themetered materials into the mold through the nozzle 21.

In the second embodiment of the apparatus as above, the plunger 24 maybe modified so as to have an enlarged part and a screw thread such asthe screw thread (25 and 29) of FIG. 1. Further only an enlarged partsuch as that (25) of FIG. 4 may be integrated with the plunger 24.

FIG. 8, FIG. 9 and FIG. 10 show modified check valve means incorporatedwith the double barrel type apparatus as shown in FIG. 7.

Referring to FIG. 8, the modification resides in that the front open endof the inner barrel 22B has a conical shape having a central holeintegral with the hollow of the barrel 22B. The tapered open end has aconical inner surface 44. The plunger 24 has a tapered head having aninclined surface. The tapered plunger head is located in the innerbarrel 22B and forms a movable valve member, while the conical open endof the inner barrel 22B forms a valve seat. The valve comprised of thevalve seat and the valve chamber is closed when the plunger 24 is movedforward relative to the inner barrel 22B thereby engaging the plungerhead 24 with the conical end of the inner barrel 22B.

Referring to FIG. 9, the modified check valve comprises a valve chamberformed in the front end of the inner barrel 22B, which is open to theouter barrel 22A through a narrow passage 46 and also to the interior ofthe inner barrel 22B through a constricted passage. A check ball 48 ismovably received in the valve chamber to form a movable valve member.The valve chamber has a front inner surface having grooves 49 formedtherein to communicate with the narrow passage 46. While the ball 48 isin contact with the front inner surface of the valve chamber, the valveis open to allow the materials to enter through the grooves 49 and thenarrow passage into the metering chamber located in front of the innerbarrel 22B. When the inner barrel 22B is actuated to inject the meteredmaterials into the mold, the ball 48 is forced by the metered materialsto move rearward to the rear surface of the valve chamber to therebyclose the valve.

Referring to FIG. 10, the inner barrel 22B has a front end portionforming a valve chamber having a through-hole passage 46. A conventionalmovable valve member 50 is pivotally mounted in the valve chamber. Anactuator (not shown) is provided to drive the valve member 50 to therebyclose the valve.

FIG. 11 and FIG. 12 show other embodiments of the present invention.Both of these embodiments relate to a single barrel type injectionapparatus as shown in FIG. 1, with a check valve means modified fromthat of FIG. 1.

Referring to FIG. 11, a jack stuffer 27 is provided to be incorporatedwith a valve chamber in substantially the same manner as that of FIG. 9.The valve means comprises a valve chamber 28 and a movable ball valvemember 51 received therein, and is located between a feed inlet open toa rear portion of the barrel 22 and the feed outlet of the stuffer 27 tocommunicate with the barrel and the stuffer. The plunger 24 has anenlarged rear portion slidably and rotatably fitted in the inner surfaceof the barrel, and a front portion located in the barrel 22 with a spacegap therebetween. A metering chamber is defined by the interior of thebarrel 22 and the front portion of the plunger 24. When the stuffer 27feeds the materials, the ball 52 is in contact with the barrel sideinner surface of the valve chamber, and this contact keeps the valveopen. When the materials in the metering chamber are injected into themold by the action of the plunger 24, the ball 52 is forced into contactwith the stuffer side inner surface of the valve chamber by a pressureexerted by the metered materials, until the enlarged rear portion of theplunger 24 covers the feed inlet of the barrel 22, to thereby close thevalve.

Referring to FIG. 12, a vertical jack stuffer 27 is provided to have anadditional cylindrical portion 53 coaxial with the barrel 22, at thepoint where the barrel 22 is rotatably and slidably disposed. Thecylindrical portion 53 communicates with a feed outlet 58 of the stuffer27. A rotatable barrel 22 is provided having a feed inlet opening 57covered by the additional stuffer portion 53. A sealing 53a is providedbetween the barrel 22 and the additional stuffer portion 53 to preventthe feed materials from leaking out of the stuffer 27. The feed inletopening 57 is designed so as to communicate with the feed outlet 58 ofthe stuffer 2 when the rotatable barrel 22 is positioned at a specificangle, as shown in FIG. 13, and to be covered by the wall of theadditional stuffer portion 53 when the rotatable barrel 22 is positionedat another angle, for example, 45° from the above specific angle, asshown in FIG. 14.

A motor 56 is provided to rotate the barrel 22 by means of atransmission including a rack 54 and a pinion 55. While the materialsare fed into the barrel 22, the check valve is opened by keeping thebarrel at the specific angle. When the injection is carried out, thevalve is closed by setting the barrel 22 to the other angle.

With the double barrel type apparatus as shown in FIGS. 7 to 10, a checkvalve means as that of FIG. 11 or FIG. 12 may be alternatively employedin place of the valve means provided in this apparatus.

Further, with the apparatus as shown in FIGS. 7 to 12, the plunger 24may have a screw thread such as the before mentioned screw thread 26 ora projection such as the before mentioned projection 32.

With respect to the apparatus involving the screw thread 26, the plunger24 with the screw thread 26 formed thereon is supported only at its rearend. In this regard, the plunger 24 is subjected to a biased weight dueto the action of the feed materials forced in by the jack stuffer 27,with the result that the plunger supporting portion involved is liableto wear or seizure. To prevent such an unfavorable phenomenon, it ispreferable to adopt the following feeding and metering operation. First,the plunger 24 is rotated so that the feed materials fill a localcircumferential space around the plunger 24 in the vicinity of the feedoutlet of the stuffer 27. Then, while the rotation continues, the jackstuffer 27 is actuated to extrude the materials into the barrel 22.

Further, to prevent a terminating portion of the plunger 24 (or theplunger with the inner barrel 22B) from being deviated from apredetermined position in the metering process, the followingcountermeasures may be adopted.

1. About 5 to 50 mm before a predetermined metering stroke of theplunger is attained, a pressure exerted by the jack stuffer is reducedto zero, in the alternative ways described below in items 2 to 4.

2. In the process of item 1 above, the stuffer pressure is reduced in astep manner.

3. In the process of item 1 above, a feed speed is fed back asinformation for reducing the pressure in a step manner.

4. In the process of item 1 above, a time when the metering terminatesis predicted from a metering speed, and the stuffer pressure is reducedin a step manner with each step being carried out in advance at apredetermined period of time calculated from the predicted time data.

5. In place of the above presure reducing process, the r.p.m. of theplunger is reduced rapidly or in a step manner. This process may becarried out concurrently with the pressure reducing process.

6. When the metering terminates or just before the termination, the jackplunger of the stuffer is stopped and is then moved back.

7. When the metering terminates or just before the termination, theplunger is subjected to an increased back pressure so that the plungeris prevented from moving back from the metering position.

8. A pressure applied to the jack plunger of the stuffer is controlledaccording to the volume of mate rials in the stuffer, to adjust thedensity of the material to a predetermined level. That is, when thevolume of the materials is large, the pressure is increased, and whenthe volume of the materials is decreased, the pressure is reducedaccordingly.

The advantageous feature of the apparatus of the present inventionresides in that the metering and feeding process does not damage thefibers contained in the reinforced materials, i.e., the fibers in thematerials are not cut or bent. Further the materials are assuredlyinjected in the feeding order without substantial interchange among theleading feed material parts and subsequent or following feed materialparts in the barrel. Under these circumstances, very little of thematerials remains, and a back flow of the materials is prevented. Inthis connection, the amount of a shot is always stable. Further, themetering becomes considerably stable due to appropriate controls of ther.p.m. of the plunger, a pressure exerted by the jack plunger of thestuffer against the materials and a back pressure applied against thefeed materials, and air entrainment with the materials is reduced.

During experiments with the apparatus of the present invention, therewas a case where BMC was fed into the barrel 22 due to action of thejack stuffer 27 without cooperation of the plunger due to a rotationthereof. In this case, most of the materials fed were forced to remainat local positions in the barrel, with the result that the materialswere not moved smoothly forward, and thus the metering process wasextremely degraded. In this case, an increased extrusion pressure of thejack stuffer 27 did not improve the metering performance.

However, in cases where the plunger 24 was rotated at a relatively lowspeed, such as 25 to 150 r.p.m., while BMC was fed by the action of thejack stuffer 27, BMC was smoothly transferred forward through the barreland the metering was smoothly and assuredly performed.

A comparison of impact strength was made between molded productsinjected by the plunger type apparatus according to the presentinvention and those injected by a conventional screw plunger typeinjection apparatus. The result was that the products according to thepresent invention had an impact strength of 13 kg-cm/cm², while theproducts of the prior art had an impact strength of 8 kg-cm/cm².

Where different reinforced materials were used in the above two kinds ofapparatus, the resultant products of the present invention had an impactstrength of 18 kg-cm/cm², while the products of the prior art had animpact strength of 11 kg-cm/cm².

We claim:
 1. An injection molding apparatus for injecting athermosetting resin having glass fibers into a mold, comprising:acylindrical barrel having a central axis and a tapered first end formingan injection nozzle; supply means for injecting a predetermined flow ofthe thermosetting resin into said cylindrical barrel, said supply meansincluding an outlet port extending axially along said barrel; plungermeans disposed within said barrel for channeling the thermosetting resintoward said injection nozzle and for injecting the thermosetting resinthrough said injection nozzle, said plunger means including an elongatedplunger and motor means connected to said plunger at a second end ofsaid barrel for selectively rotating and reciprocating said plungerabout the axis of said barrel, said plunger means including a plungerhead at an end of said plunger facing said injection nozzle, groovemeans along the periphery of said plunger substantially adjacent saidplunger head, and a check ring slidably and rotatably confined withinsaid barrel along said groove means to admit the thermosetting resininto an expandable metering chamber extending between said injectionnozzle and said plunger head, said check ring also preventing a backflowof the thermosetting resin from said metering chamber, said plungerhaving a peripheral portion between said groove means and said outletport of said supply means sized to have a cross section narrower thanthe diameter of said cylindrical barrel, said peripheral portion andsaid barrel defining a continuous annular gap between said groove meansand said outlet port to channel the thermosetting resin containing theglass fibers into said metering chamber; and means for generating backpressure within said barrel to urge said plunger toward said second endfurther filling said metering chamber with the thermosetting resin, themetered resin being injected through axial movement of said plunger inthe direction of said injection nozzle.
 2. An injection moldingapparatus for injecting a thermosetting resin having glass fibers into amold, comprising:a cylindrical barrel having a central axis and atapered first end forming an injection nozzle; supply means forinjecting a predetermined flow of the thermosetting resin into saidcylindrical barrel, said supply means including an outlet port extendingaxially along said barrel; plunger means disposed within said barrel forchanneling the thermosetting resin toward said injection nozzle and forinjecting the thermosetting resin through said injection nozzle, saidplunger means including an elongated plunger and motor means connectedto said plunger at a second end of said barrel for rotating andreciprocating said plunger about the axis of said barrel, said plungerincluding a first helical extension extending radially and axiallyaround a peripheral portion of said plunger at a first angle, saidhelical extension being axially aligned with said outlet port of saidsupply means to rotate and reciprocate proximate said outlet portdirecting the resin admitted through said outlet port toward said firstend, said plunger means also including a plunger head at an end of saidplunger facing said injection nozzle, groove means disposed along saidplunger substantially adjacent said plunger head, and a check ringslidably and rotatably confined within said barrel along said groovemeans to admit the thermosetting resin into an expandable meteringchamber extending between said injection nozzle and said plunger head,said check ring also preventing a backflow of the thermosetting resinfrom said metering chamber, said plunger having a peripheral portionbetween said groove means and said first helical extension sized to havea cross section narrower than the diameter of said cylindrical barrel,said peripheral portion and said barrel defining a continuous annulargap between said groove means and said outlet port to channel thethermosetting resin containing the glass fibers directed by said firsthelical extension into said metering chamber; and means for generatingback pressure within said barrel to urge said plunger toward said secondend further filling said metering chamber with the thermosetting resin,the metered resin being injected through axial movement of said plungerin the direction of said injection nozzle.
 3. The injection moldingapparatus according to claim 2, wherein said supply means includes astuffer chamber extending from said outlet port, and wherein a planeextending through a center of said stuffer chamber is alignedsubstantially perpendicular to the axis of said barrel, said stufferchamber having an inlet port and housing a reciprocating stuffer plungerto urge said predetermined flow of the thermosetting resin admittedthrough said inlet port toward said outlet port.
 4. The injectionmolding apparatus according to claim 2, wherein said first helicalextension extends not more than 360° around the periphery of saidplunger.
 5. The injection molding apparatus according to claim 2,wherein said means for generating back pressure includes an annular ringextending from said plunger and frictionally engaging said barrelbetween said outlet port and said second end.
 6. The injection moldingapparatus according to claim 5, wherein said plunger means also includesa second helical extension extending radially and axially around aperipheral portion of said plunger between said annular ring and saidsecond end, said second helical extension disposed at a second angle todischarge any resin urged between said annular ring and said barrel atsaid second end.